Pressure-sensitive adhesive tape is generally manufactured by coating onto a backing sheet a solution or emulsion of a pressure-sensitive adhesive polymer. The equipment necessary to drive off the volatile vehicle is usually very expensive, including elaborate drying ovens and massive ducting. The evolved vehicle tends to pollute the atmosphere, even if it is primarily water, unless the ovens are equipped to recover the pollutants. Such recovery equipment is expensive both to construct and to operate.
Belgian Pat. No. 675,420 which was published May 16, 1966, concerns a process for making pressure-sensitive adhesive tape which evolves no volatile vehicle. While maintaining an inert atmosphere, a mixture of acrylic monomers is coated onto a backing sheet and then polymerized in situ to a pressure-sensitive adhesive state. In each of the examples, the polymerization is initiated by ultraviolet radiation. The monomer mixture of Example 1 consists of 90 parts ethylhexyl acrylate, 5 parts acrylic acid and 5 parts polyvinylisobutyric acid. This and the acrylic monomer mixtures of each of the other examples are so low in viscosity as to make it difficult to obtain uniform coatings. The patent suggests that to increase the viscosity, the monomer mixture can be pre-polymerized prior to coating, either by ultraviolet radiation or by any other means. If polymerized by ultraviolet radiation, an inert atmosphere would be necessary.
U.S. Pat. No. 4,181,752 (Martens et al.) discloses a process for making a pressure-sensitive adhesive by polymerizing a radiation-sensitized solventless liquid mixture containing as a major proportion thereof at least one acrylic acid ester of an alkyl alcohol, said alcohol containing from 4 to 14 carbon atoms. The mixture preferably includes at least one monomer copolymerizable therewith. The process is similar to that of Belgian Pat. No. 675,420 except that the Belgian patent discloses nothing of the specific intensity and the specific spectral distribution of the irradiation. U.S. Pat. No. 4,181,752 discloses that these must be controlled in order to attain desirably high cohesive strength and also to attain high peel resistance, namely, to subject the polymerizable mixture to radiation in the near ultraviolet region at a rate of irradiation in the 3000-4000 Angstrom wavelength range of not more than 7 milliwatts per square centimeter of the mass exposed, said radiation allowably also containing incidental radiation energy, the amount of said incidental radiation energy having wavelengths shorter than 3000 Angstroms being limited to not more than about 10% of the amount of energy in the 3000-4000 Angstrom range. Because the same specific intensity and specific spectral distribution of the irradiation are preferred for the practice of the present invention, the disclosure of U.S. Pat. No. 4,181,752 is here incorporated by reference.